Solar calculators · FREE TOOL

Solar Panel Size Calculator

Estimate array wattage for a daily energy target, then round up to whole panels and see the corresponding production estimate.

1

Your inputs

Edit the example
Core inputs
Wh/day
h/day
W

Leave blank for an array-wattage estimate without a panel count.

Planning assumptions
%

Example estimate · editable inputs

Required array rating

1,600 W

Whole panels (rounded up)
4 panels
Rounded array
1,600 W
Resulting daily production
6,800 Wh/day

Energy estimate only. Seasonal shortfalls, installation constraints and storage require separate assessment.

BEHIND THE RESULT

How the calculation works

Required array W = daily Wh ÷ (peak sun hours × performance factor). Panel count = round up(array W ÷ individual panel W).

Whole-panel rounding provides a discrete equipment count. A seasonal energy shortfall can still occur even when average estimated production meets the target.

A worked example

6,800 Wh/day at 5 peak sun hours and an 85% factor needs 1,600 W of panels: four 400 W panels. A 7,000 Wh/day target rounds up to five panels, with an estimated 8,500 Wh/day.

What this estimate can’t tell you

No roof engineering, wiring design, structural review, permitting, mounting assessment or installation certification. Storage and charging constraints are separate.

Sources & methodology

Formulas are derived from the units shown. Read our methodology or report a correction. Sources reviewed 2026-11-01.